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Bacteria and Viruses Biology II: Chapter 19 Prokaryotes • Single-celled organisms that lack a nucleus • Circular DNA • Range in size from 1-5 micrometers • (Eukaryotic cells range in size from 10-100 micrometers) • Exceptions! Epulopiscium fisheloni, a giant prokaryote 500 micrometers long! Classifying Prokaryotes • Used to be kingdom Monera • We now know we can divide them into 2 domains and 2 kingdoms Domain Bacteria: Kingdom Eubacteria • What we think about when we say “bacteria” • The larger of the two domains of prokaryotes • Includes a wide range of organisms with different lifestyles • Live almost anywhere Domain Bacteria: Kingdom Eubacteria • Surrounded by a cell wall that protects the cell from injury and determines its shape • Cell well contains peptidoglycan (murein) – made of sugars and amino acids Domain Bacteria: Examples • Cyanobacteria: photosynthetic, like plants, which means that they use the sun’s energy to make food for themselves. • Spirochetes: are gram-negative spiral-shaped, and heterotrophic. Some of them live in the presence of oxygen, others don’t. • Gram-positive bacteria: includes the strain of streptococcus bacteria that causes strep throat. It also includes the bacteria that produces yogurt, by growing and fermenting in milk (producing lactic acid). These bacteria also produce many of our antibiotics. • Proteobacteria: is one of the largest phyla of all the bacteria. Many are gram-negative. They are divided into several subgroups, such as enteric bacteria, chemoautotrophs, and nitrogen-fixing bacteria. The enteric bacteria live mainly in intestinal tracts, like E. coli. Domain Archaea: Kingdom Archaebacteria • Under a microscope look similar to eubacteria • Equally small, lack nuclei, and have cell walls • Lack peptidoglycan • Membrane lipids are quite different Domain Archaea: Kingdom Archaebacteria • Archaebacteria are found in very harsh conditions (such as at the bottom of the sea or in volcanic vents) • This is thought to be because the early Earth’s atmosphere was filled with poisonous gases and was very hot – nothing could survive, except the archaebacteria. • Obligate anaerobes, meaning they cannot live in the presence of oxygen Domain Archaea: Examples • Methanogens: are characterized by their ability to harvest energy by converting H2 and CO2 into methane gas; found in marshes and in the intestinal tracts of humans and some animals • Halophiles: salt-loving; found in the Dead Sea, the Great Salt Lake, and other areas with a high salt content • Thermoacidophiles: found in extremely acidic conditions and in areas with very high temperatures. They can survive in areas with temperatures as high as 230ₒF and with pHs below 2; locations include volcanic vents and hydrothermal vents (cracks in the ocean floor where scalding water leaks out) Archaea to Eukarya • The DNA of archaebacteria genes are more like those of eukaryotes than those of eubacteria • Scientists believe they may be the ancestors of eukaryotes Identifying Prokaryotes • Shape • Cell wall chemical structure • Movement • Energy obtainment Prokaryote Shape • Bacilli – Rod-shaped • Cocci – Spherical-shaped • Spirilla – Spiral and corkscrew-shaped Gram Staining • All eubacteria are classified by gram staining • Determines many things – resistance to antibiotics, for one thing – identify an unknown bacteria • Staining a group of bacteria with four different liquids Gram Positive: Purple • Cell wall containing many peptidoglycan, which absorbs the gram stain. • Much more susceptible to antibiotics than gram-negative bacteria because they are not selectively permeable Gram Negative: Red • Cell wall containing a second, outer layer of lipid and carbohydrate molecule • Selectively permeable and gram stain cannot pass through Prokaryote Movement • Flagella • Lash • Snake • Spiral • Move on a slime trail • No movement at all Prokaryote Energy Obtainment 1. Photoautotroph: carry out photosynthesis in a manner similar to green plants • Live near the surface of lakes, streams, and oceans • Cyanobacteria: found around the world in freshwater, saltwater and on land Prokaryote Energy Obtainment 2. Chemoautotroph: obtain energy from inorganic materials • Many obtain energy from chemicals in deep sea vents Prokaryote Energy Obtainment 3. Heterotroph: organism that obtains energy from taking in organic molecules and then breaking them down; a consumer 4. Photoheterotroph: photosynthetic organisms that also need organic compounds for nutrition Releasing Energy • Bacteria need a constant supply of energy released by cellular respiration (with O2) & fermentation (without O2) • Obligate aerobes: need O2 to survive • Obligate anaerobes: die in the presence of O2 • Facultative anaerobes: survive with or without O2 Growth and Reproduction • When conditions are favorable, prokaryotes can grow and divide at astonishing rates • Some divide as often as every 20 minutes! Reproduction: Binary Fission • Asexual reproduction • Prokaryote replicates its DNA • Divides in half, produces two identical daughter cells Reproduction: Conjugation • Sexual reproduction • Paramecia and some prokaryotes • Exchange genetic information through a hollow bridge Reproduction: Endospore • Formed when conditions become unfavorable for reproduction • Bacterium produces a thick internal wall • Wall encloses its DNA and a portion of its cytoplasm to remain dormant until good conditions arise Bacteria in Nature • Bacteria are vital to maintaining the living world • Some producers that capture energy by photosynthesis • Other help to break down the nutrients in dead matter and the atmosphere, allowing other organisms to use the nutrients Decomposers • Help the ecosystem recycle nutrients • When a tree dies and falls to the forest floor, armies of bacteria attack and digest the dead tissue • The bacteria break the dead matter into simpler substances, which are released into the soil and taken up by the plants (picture: food in human digestive tract) Nitrogen Fixers • Plants and animals depend on bacteria for nitrogen (amino acids proteins) • 80% of the atmosphere is nitrogen gas Nitrogen Fixers • Plants need nitrogen in the form of ammonia • Certain bacteria are able to convert nitrogen • Nitrogen Fixation: process of converting nitrogen gas into ammonia Bacteria and Disease • Some damage the tissues of the infected organism directly by breaking them down for food • Other bacteria release toxins (poisons) that harm the body Antibiotics • Compounds that block the growth and production of bacteria • Can be used to cure many bacterial diseases Human Uses of Bacteria: Foods • Cheese • Pickles • Yogurt • Sauerkraut • Buttermilk • Vinegar from wine • Sour cream Human Uses of Bacteria: Industry • Digest petroleum (helpful in cleaning up oil spills) • Remove waste products and poisons from water • Mine minerals from the ground • Synthesize drugs and chemicals through genetic engineering Controlling Bacteria • Most bacteria are harmless and beneficial • The risks of bacterial infections are great enough to warrant efforts to control bacterial growth • Sterilization: destroys bacteria by subjecting them either to great heat or chemical action What is a Virus? • A particle made up of: – Nucleic acid – Protein – And in some cases lipids What is a Virus? • Replicate only by infecting living cells • Differ widely in size and structure • One thing in common: enter living cells and, once inside, use the machinery of the infected cell to produce more viruses Viruses • Most viruses are so small that they can only be seen with a microscope • A typical virus: – Composed of a core of either DNA or RNA – DNA or RNA is surrounded by a protein coat, or capsid Capsid • The capsid proteins bind to the surface of a cell • The proteins “trick” the cell into allowing it inside Capsid • The viral genes take over the cell • The cell transcribes the viral genes, putting the genetic program of the virus into effect • Often times the virus destroys the cell Viral Infection • Viruses must bind precisely to proteins on the cell surface and then use the host’s genetic system • Most viruses are highly specific to the cells they infect • Bacteriophage: a virus that infects bacteria Lytic Infection • A virus enters a cell, makes a copy of itself, and causes the cell to burst • Example: Bacteriophage T4 has a DNA core inside an intricate capsid that is activated by contact with a host cell Lytic Infection • T4 injects its DNA into the host • Usually the host cannot tell that the DNA is foreign and ends up copying the viral DNA! • The infected cell lyses, or bursts, and releases hundreds of virus particles that may go on to infect other cells Lysogenic Infection • A virus embeds its DNA into the DNA of the host cell and is replicated along with the host cell’s DNA • Prophage: the DNA that is embedded in the host’s DNA • Infection that causes the host cell to make copies of the virus indefinitely Lysogenic Infection • Example: Bacteriophage lambda causes a lysogenic infection • Lysogenic viruses do not lyse the host cell right away • Eventually the viral DNA will remove itself from the host DNA and direct the synthesis of new virus particles Viruses and Disease • Polio, measles, AIDS, mumps, influenza, yellow fever, rabies, the common cold • In most viral infections, viruses attack and destroy certain cells in the body, causing the symptoms of the disease Viruses and Disease • Vaccines are used to prevent infection – A weakened or killed virus or viral proteins that stimulates the immune system to produce immunity to the disease – Most vaccines provide protection only if used before an infection begins Viruses and Cancer • Oncogenic viruses cause cancer in animals • Carry genes that disrupt the normal controls over cell growth and division • By studying such viruses, scientists have identified many of the genes that regulate cell growth in eukaryotes Retroviruses • Viruses that contain RNA as their genetic information • When infecting a cell, retroviruses produce a copy of DNA from a copy of their RNA • This DNA is inserted in the host DNA Retroviruses • The name “retrovirus” comes from the fact that their genetic information is copied backward-from RNA to DNA • Responsible for some types of cancer in animals • HIV is a retrovirus Prions • Infectious particle made up of a misfolded protein rather than RNA or DNA • Prions accumulate, especially in the nervous system, that cells become damaged or destroyed • Prions are resistant to heat and digestive enzymes, so they are not destroyed by cooking infected meat Mad Cow Disease • In 1985, veterinarians in Great Britain found cows suffering from a disease that, like scrapie in sheep, attacked and destroyed parts of the brain • BSE (for "bovine spongiform encephalopathy"), but the erratic behavior of infected cattle led to the common name of "mad cow disease" • When evidence emerged that mad cow disease and Creutzfeldt-Jakob disease (CJD), a similar disease in humans, might be caused by prions, people began to worry. • Was it possible that more than 100 people in Britain had died from CJD caused by prion-infected beef? Mad Cow Disease • In 1996, British authorities concluded that the practice of using tissue from sheep and cows to prepare cattle feed had made it possible for BSE to spread rapidly to cattle and then to humans who ate contaminated beef. • They banned the use of cattle tissue in feed, and a similar ban was put in force in the United States the very next year. • In 2002, however, BSE was discovered in cows in Canada, and near the end of 2003, tissue from a Washington state cow with BSE was discovered after its meat had been processed. What is 2009 H1N1 (swine flu)? • A new influenza virus causing illness in people • First detected in people in the United States in April 2009 • Spreading from person-to-person worldwide, probably in much the same way that regular seasonal influenza viruses spread • June 11, 2009, the World Health Organization (WHO) signaled that a pandemic of 2009 H1N1 flu was underway Why is H1N1 called “swine flu”? • Laboratory testing showed that many of the genes in this new virus were very similar to influenza viruses that normally occur in pigs (swine) in North America • Further study has shown that it is very different from what normally circulates in North American pigs • It has two genes from flu viruses that normally circulate in pigs in Europe and Asia and bird (avian) genes and human genes • two proteins found on the surface of the virus: hemagglutinin (H) and neuraminidase (N) How does 2009 H1N1 virus spread? • Spread of 2009 H1N1 virus is thought to occur in the same way that seasonal flu spreads • Person to person – coughing or sneezing – touching something – such as a surface or object – with flu viruses on it and then touching their mouth or nose What are the signs and symptoms of this virus in people? • • • • • • Fever Cough Sore throat Runny or stuffy nose Body aches Headache • • • • • Chills Fatigue Diarrhea Vomiting Severe illnesses and death How long can an infected person spread this virus to others? • 1 day before getting sick to 5 to 7 days after. • This can be longer in some people, especially children and people with weakened immune systems What can I do to protect myself from getting sick? • Vaccination BEFORE sickness • Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it. • Wash your hands often with soap and water, especially after you cough or sneeze. • Avoid touching your eyes, nose or mouth. Germs spread this way. • Try to avoid close contact with sick people. • If you are sick with flu-like illness, stay home for at least 24 hours after your fever is gone except to get medical care or for other necessities. Are Viruses Alive? • NO. • Viruses share the genetic code with living things and affect living things • They do not have all the characteristics of life (chapter 1) • They are not cells • Not able to reproduce independently • However, when they infect living cells they can make copies of themselves, even evolve